1. Technical Field
The present invention relates to syringe devices used to inflate balloon-tipped catheters, such as coronary angioplasty dilatation catheters, and more particularly to a syringe apparatus having a pressure gauge mounted thereto.
2. Background Information
An important tool in present medical procedures is the use of balloon-tipped catheters. Numerous configurations of balloon-tipped catheters have been developed for particular medical procedures. For purposes of simplicity and brevity, the following discussion will be directed to the use of a particular type of balloon-tipped catheter generally known as coronary angioplasty dilatation catheters.
Following the first primitive experiments in coronary angioplasty in the 1970s, coronary angioplasty quickly received widespread attention as an alternative to coronary bypass surgery. Coronary bypass surgery involves surgical access to the heart, placing the patient on an extracorporeal blood oxygenation system so that the heart can be stopped for surgery, and then surgically attaching one or more passageways to bypass a clogged coronary artery, all under a general anesthetic. Coronary angioplasty, generally performed under a local anesthetic, involves running a dilatation catheter (a catheter having an inflatable balloon near the end) to the diseased blood vessel and then inflating the balloon in order to open the passageway, thereby obtaining increased blood flow. The angioplasty procedure typically involves less risk to the patient, and significantly lessens the patient's discomfort and recovery time.
Of great importance during an angioplasty procedure is to take notice that during inflation of the dilatation catheter, no blood can flow through the blood vessel being mechanically dilated. Clearly, the disruption of blood flow must be limited in duration so as to avoid tissue damage due to oxygen deprivation. Hence, it is important to insure that the balloon is deflated and blood flow restored before tissue damage can occur. In most cases, it is not possible to adequately dilate a diseased blood vessel in a single inflation. In cases where it is necessary to undertake multiple inflations in the same location it is important to allow sufficient time between successive inflations so that the tissues fed by the diseased blood vessel can become fully oxygenated before blood flow is disrupted again.
At the same time, it is important to the success of the procedure that the dilation of the vessel be permitted to extend for a significant period of time. Although specific techniques can vary significantly depending upon the nature of the blockage, the catheter being used, and the like, the most common technique involves inflating the catheter relatively rapidly and then leaving it in place for several minutes. Although it might be proposed to use very short intervals of inflation in order to minimize the risk due to oxygen deprivation, followed by long intervals of deflation, it has been found to be better to utilize very long intervals of inflation in order to achieve the most effective dilation of the diseased blood vessel, and short intervals of deflation in order to bring the procedure to a conclusion more rapidly. The typical angioplasty procedure compromises these two factors by maintaining the balloon in the inflated and deflated conditions for a moderate amount of time.
In order to insure the success of the procedure without damage to the tissues fed by the diseased blood vessel, it is critical to monitor the duration of each inflation and deflation. It is also important that the physician performing the angioplasty have access to historical information regarding the duration of past inflations and deflations. In the past, this information has typically been recorded manually. Commonly, the operator of the syringe used to apply the inflation pressure will call out as pressure is applied and the time is noted by an assistant, or the assistant activates a stopwatch. The assistant continuously monitors the time and informs the catheterization team as required. At the appropriate time, as determined by the directing physician, the syringe operator deflates the catheter while the assistant monitors the deflation time. The assistant also maintains a record of the duration of each inflation and deflation. At any given time, the directing physician can learn of the duration of the most recent inflation or deflation, and the history of past inflations and deflations by asking the assistant.
Obviously, this process is somewhat cumbersome, and is also subject to errors in computing durations, while recording the information, or reporting it as required. This is particularly so when the assistant has other significant duties. Yet, it is quite expensive to dedicate an assistant solely for the function of monitoring and recording times.
One approach to dispensing with the function of the assistant in monitoring times has been to utilize computers to serve that function. For example, one approach has been to incorporate a pressure transducer into the syringe system used to inflate the balloon-tipped catheter. A computer is then used to monitor the pressure transducer to mark changes in pressure corresponding to inflation and deflation, and the duration of each such pressure change. The difficulty with this approach is that although very accurate and reliable, it is expensive, and some angioplasty facilities are unable to afford to purchase one. This approach also involves the use of yet another instrument, and some directing physicians are unwilling to add another instrument to the already very cluttered angioplasty operating theater. Despite the serious shortcomings of the original system using an assistant to monitor and record times of inflation and deflation, facilities and physicians finding themselves unable or unwilling to add a computerized monitor have had no alternatives.